Dynamically load a JavaScript file

How can you reliably and dynamically load a JavaScript file? This will can be used to implement a module or component that when 'initialized' the component will dynamically load all needed JavaScript library scripts on demand.

The client that uses the component isn't required to load all the library script files (and manually insert <script> tags into their web page) that implement this component - just the 'main' component script file.

How do mainstream JavaScript libraries accomplish this (Prototype, jQuery, etc)? Do these tools merge multiple JavaScript files into a single redistributable 'build' version of a script file? Or do they do any dynamic loading of ancillary 'library' scripts?

An addition to this question: is there a way to handle the event after a dynamically included JavaScript file is loaded? Prototype has document.observe for document-wide events. Example:

document.observe("dom:loaded", function() {
  // initially hide all containers for tab content
  $$('div.tabcontent').invoke('hide');
});

What are the available events for a script element?

标签： javascript file import include

24条回答

大哥的爱人

2楼-- · 2018-12-31 10:49

I did basically the same thing that you did Adam, but with a slight modification to make sure I was appending to the head tag to get the job done. I simply created an include function (code below) to handle both script and css files.

This function also checks to make sure that the script or CSS file hasn't already been loaded dynamically. It does not check for hand coded values and there may have been a better way to do that, but it served the purpose.

function include( url, type ){
    // First make sure it hasn't been loaded by something else.
    if( Array.contains( includedFile, url ) )
        return;

    // Determine the MIME-type
    var jsExpr = new RegExp( "js$", "i" );
    var cssExpr = new RegExp( "css$", "i" );
    if( type == null )
        if( jsExpr.test( url ) )
            type = 'text/javascript';
        else if( cssExpr.test( url ) )
            type = 'text/css';

    // Create the appropriate element.
    var tag = null;
    switch( type ){
        case 'text/javascript' :
            tag = document.createElement( 'script' );
            tag.type = type;
            tag.src = url;
            break;
        case 'text/css' :
            tag = document.createElement( 'link' );
            tag.rel = 'stylesheet';
            tag.type = type;
            tag.href = url;
            break;
    }

    // Insert it to the <head> and the array to ensure it is not
    // loaded again.
    document.getElementsByTagName("head")[0].appendChild( tag );
    Array.add( includedFile, url );
}

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不再属于我。

3楼-- · 2018-12-31 10:49

another awesome answer

$.getScript("my_lovely_script.js", function(){


   alert("Script loaded and executed.");
  // here you can use anything you defined in the loaded script

 });

https://stackoverflow.com/a/950146/671046

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情到深处是孤独

4楼-- · 2018-12-31 10:49

i've used yet another solution i found on the net ... this one is under creativecommons and it checks if the source was included prior to calling the function ...

you can find the file here: include.js

/** include - including .js files from JS - bfults@gmail.com - 2005-02-09
 ** Code licensed under Creative Commons Attribution-ShareAlike License 
 ** http://creativecommons.org/licenses/by-sa/2.0/
 **/              
var hIncludes = null;
function include(sURI)
{   
  if (document.getElementsByTagName)
  {   
    if (!hIncludes)
    {
      hIncludes = {}; 
      var cScripts = document.getElementsByTagName("script");
      for (var i=0,len=cScripts.length; i < len; i++)
        if (cScripts[i].src) hIncludes[cScripts[i].src] = true;
    }
    if (!hIncludes[sURI])
    {
      var oNew = document.createElement("script");
      oNew.type = "text/javascript";
      oNew.src = sURI;
      hIncludes[sURI]=true;
      document.getElementsByTagName("head")[0].appendChild(oNew);
    }
  }   
}

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若你有天会懂

5楼-- · 2018-12-31 10:50

I wrote a simple module that automatizes the job of importing/including module scripts in JavaScript. Give it a try and please spare some feedback! :) For detailed explanation of the code refer to this blog post: http://stamat.wordpress.com/2013/04/12/javascript-require-import-include-modules/

var _rmod = _rmod || {}; //require module namespace
_rmod.on_ready_fn_stack = [];
_rmod.libpath = '';
_rmod.imported = {};
_rmod.loading = {
    scripts: {},
    length: 0
};

_rmod.findScriptPath = function(script_name) {
    var script_elems = document.getElementsByTagName('script');
    for (var i = 0; i < script_elems.length; i++) {
        if (script_elems[i].src.endsWith(script_name)) {
            var href = window.location.href;
            href = href.substring(0, href.lastIndexOf('/'));
            var url = script_elems[i].src.substring(0, script_elems[i].length - script_name.length);
            return url.substring(href.length+1, url.length);
        }
    }
    return '';
};

_rmod.libpath = _rmod.findScriptPath('script.js'); //Path of your main script used to mark the root directory of your library, any library


_rmod.injectScript = function(script_name, uri, callback, prepare) {

    if(!prepare)
        prepare(script_name, uri);

    var script_elem = document.createElement('script');
    script_elem.type = 'text/javascript';
    script_elem.title = script_name;
    script_elem.src = uri;
    script_elem.async = true;
    script_elem.defer = false;

    if(!callback)
        script_elem.onload = function() {
            callback(script_name, uri);
        };

    document.getElementsByTagName('head')[0].appendChild(script_elem);
};

_rmod.requirePrepare = function(script_name, uri) {
    _rmod.loading.scripts[script_name] = uri;
    _rmod.loading.length++;
};

_rmod.requireCallback = function(script_name, uri) {
    _rmod.loading.length--;
    delete _rmod.loading.scripts[script_name];
    _rmod.imported[script_name] = uri;

    if(_rmod.loading.length == 0)
        _rmod.onReady();
};

_rmod.onReady = function() {
    if (!_rmod.LOADED) {
        for (var i = 0; i < _rmod.on_ready_fn_stack.length; i++){
            _rmod.on_ready_fn_stack[i]();
        });
        _rmod.LOADED = true;
    }
};

//you can rename based on your liking. I chose require, but it can be called include or anything else that is easy for you to remember or write, except import because it is reserved for future use.
var require = function(script_name) {
    var np = script_name.split('.');
    if (np[np.length-1] === '*') {
        np.pop();
        np.push('_all');
    }

    script_name = np.join('.');
    var uri = _rmod.libpath + np.join('/')+'.js';
    if (!_rmod.loading.scripts.hasOwnProperty(script_name) 
     && !_rmod.imported.hasOwnProperty(script_name)) {
        _rmod.injectScript(script_name, uri, 
            _rmod.requireCallback, 
                _rmod.requirePrepare);
    }
};

var ready = function(fn) {
    _rmod.on_ready_fn_stack.push(fn);
};

// ----- USAGE -----

require('ivar.util.array');
require('ivar.util.string');
require('ivar.net.*');

ready(function(){
    //do something when required scripts are loaded
});

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忆尘夕之涩

6楼-- · 2018-12-31 10:51

You may write dynamic script tags (using Prototype):

new Element("script", {src: "myBigCodeLibrary.js", type: "text/javascript"});

The problem here is that we do not know when the external script file is fully loaded.

We often want our dependant code on the very next line and like to write something like:

if (iNeedSomeMore) {
    Script.load("myBigCodeLibrary.js"); // includes code for myFancyMethod();
    myFancyMethod(); // cool, no need for callbacks!
}

There is a smart way to inject script dependencies without the need of callbacks. You simply have to pull the script via a synchronous AJAX request and eval the script on global level.

If you use Prototype the Script.load method looks like this:

var Script = {
    _loadedScripts: [],
    include: function(script) {
        // include script only once
        if (this._loadedScripts.include(script)) {
            return false;
        }
        // request file synchronous
        var code = new Ajax.Request(script, {
            asynchronous: false,
            method: "GET",
            evalJS: false,
            evalJSON: false
        }).transport.responseText;
        // eval code on global level
        if (Prototype.Browser.IE) {
            window.execScript(code);
        } else if (Prototype.Browser.WebKit) {
            $$("head").first().insert(Object.extend(
                new Element("script", {
                    type: "text/javascript"
                }), {
                    text: code
                }
            ));
        } else {
            window.eval(code);
        }
        // remember included script
        this._loadedScripts.push(script);
    }
};

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公子世无双

7楼-- · 2018-12-31 10:51

I am lost in all these samples but today I needed to load an external .js from my main .js and I did this:

document.write("<script src='https://www.google.com/recaptcha/api.js'></script>");

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